Biomechanical behavior of grass roots at different gauge lengths

Gauge length influences the biomechanical properties of herbaceous roots such as tensile resistance,tensile strength and Young’s modulus.However,the extent to which and how these biomechanical properties of herbaceous roots are influenced remain unknown.To better understand the behavior of roots in tension under different conditions and to illustrate these behaviors,uniaxial tensile tests were conducted on the Poa araratica roots as the gauge length increased from 20 mm to 80 mm.Subsequently,ANOVA was used to test the impact of the significant influences of gauge length on the biomechanical properties,nonlinear regression was applied to establish the variation in the biomechanical properties with gauge length to answer the question of the extent to which the biomechanical properties are influenced,and Weibull models were subsequently introduced to illustrate how the biomechanical properties are influenced by gauge length.The results reveal that(1)the variation in biomechanical properties with root diameter depends on both the gauge length and the properties themselves;(2)the gauge length significantly impacts most of the biomechanical properties;(3)the tensile resistance,tensile strength,and tensile strain at cracks decrease as the gauge length increases,with values decreasing by 20%-300%,while Young’s modulus exhibits the opposite trend,with a corresponding increase of 30%;and(4)the Weibull distribution is suitable for describing the probability distribution of these biomechanical properties;the Weibull modulus for both tensile resistance and tensile strain at cracks linearly decrease with gauge length,whereas those for tensile strength and Young’s modulus exhibit the opposite trend.The tensile resistance,tensile strength,and tensile strain at the cracks linearly decrease with increasing gauge length,while the tensile strength and Young’s modulus linearly increase with increasing gauge length.

Biomechanical Characteristics of Rape Stalks

[Objective] To study the correlation between the biomechanical properties of rape stalks and rape stem lodging. [Method] Through axial compression tests to the stalks of 4 different rape varieties, the change rules of maximum stem bearing ca- pacity, maximum compressive strength, elastic modulus and moment of inertia along plant height were analyzed, as well as the effect of different varieties and water contents on the biomechanical property indices of rape stalks. [Result] The maximum loads of rape stalks presented liner decrease trend along with the increase of stem height, and all reached the maximums below the height of 50 cm. The maximum stem compressive strength and elastic modulus of the 4 varieties were increased with ascending height, but in a slow rate with small change, thus the modulus of e- lasticity could be considered as unchanged. The maximum bearing capacity, maxi- mum compressive strength and elastic modulus of dry rape stalks were higher than wet stalks, indicating that the water contents of rape stalks had significant effect on their mechanical properties. According to the actual lodging situations in filed, stalks of variety No. 1 owned the worst biomechanical properties and lodging degree, while the biomechanical properties of No. 6 and F5 were better than No. 1 and No. 9, and they also had stronger lodging-resistance. [Conclusion] The study provides parameters and bases for the design of mechanized production and mechanical deep processing of crops, and can better reveal the physical natures of organisms. The methods used in this study can also be used to screen excellent crop stalks.

Short and long term corneal biomechanical analysis after overnight orthokeratology

AIM: To investigate the short and long term corneal biomechanical changes after overnight orthokeratology(OK) and compare them with those occurring in subjects not wearing contact lenses.METHODS: Retrospective case control study enrolling 54 subjects that were divided into three groups 18 subjects each: control group(CG), short term(15 nights) OK(STOK) group, and long term(more than 1 y of OK wear) OK(LTOK) group. Corneal biomechanics were characterized using the Cor Vis? ST system(Oculus), recording parameters such as time [first/second applanation time(AT1, AT2)], speed [velocity of corneal apex at the first/second applanation time(AV1, AV2)], and amplitude of deformation(AD1, AD2) in the first and second corneal flattening, corneal stiffness(SPA1), biomechanically corrected intraocular pressure(b IOP) and corneal(CBI) and tomographic biomechanical indices(TBI).RESULTS: Significantly lower AD1 and standard deviate on of Ambrosio’s relational average thickness related to the horizontal profile(ARTh) values were found in the OK groups compared to CG(P<0.05). Likewise, significantly higher values of CBI were found in STOK and LTOK groups compared to CG(P<0.01). No significant differences between groups were found in integrated radius index(P=0.24), strain stress index(P=0.22), tomographic biomechanical index(P=0.91) and corneal stif fness parameter(SPA1, P=0.97). Significant inverse correlations were found between corneal thickness and CBI in STOK(r=-0.90, P<0.01) and LTOK groups(r=-0.71, P<0.01).CONCLUSION: OK does not seem to alter significantly the corneal biomechanical properties, but special care should be taken when analyzing biomechanical parameters influenced by corneal thickness such as amplitude of deformation, ARTh or CBI, because they change significantly after treatment but mainly due to the reduction and pachymetric progression induced by the corneal molding secondary to OK treatment.

A Biomechanical Comparison of Conventional versus an Anatomic Plate and Compression Bolts for Fixation of Intra-articular Calcaneal Fractures

The purpose of this study was to compare the biomechanical stability obtained by using our technique featured an anatomical plate and compression bolts versus that of the conventional anatomic plate and cancellous screws in the fixation of intraarticular calcaneal fractures.Eighteen fresh frozen lower limbs of cadavers were used to create a reproductive Sanders type-Ⅲ calcaneal fracture model by using osteotomy.The calcaneus fractures were randomly selected to be fixed either using our anatomical plate and compression bolts or conventional anatomic plate and cancellous screws.Reduction of fracture was evaluated through X radiographs.Each calcaneus was successively loaded at a frequency of 1 Hz for 1000 cycles through the talus using an increasing axial force 20 N to 200 N and 20 N to 700 N,representing the partial weight bearing and full weight bearing,respectively,and then the specimens were loaded to failure.Data extracted from the mechanical testing machine were recorded and used to test for difference in the results with the Wilcoxon signed rank test.No significant difference was found between our fixation technique and conventional technique in displacement during 20-200 N cyclic loading(P=0.06),while the anatomical plate and compression bolts showed a great lower irreversible deformation during 20-700 N cyclic loading(P=0.008).The load achieved at loss of fixation of the constructs for the two groups had significant difference:anatomic plate and compression bolts at 3839.6±152.4 N and anatomic plate and cancellous screws at 3087.3±58.9 N(P=0.008).There was no significant difference between the ultimate displacements.Our technique featured anatomical plate and compression bolts for calcaneus fracture fixation was demonstrated to provide biomechanical stability as good as or better than the conventional anatomic plate and cancellous screws under the axial loading.The study supports the mechanical viability of using our plate and compression bolts for the fixation of calcaneal fracture.

Effect of Plaque Composition on Biomechanical Performance of a Carotid Stent: Computational Study

Clinical application of bare metal stents is constrained by the occurrence of instent restenosis,mainly due to the complex biomechanical environment in the body.Numerical simulation method was used to evaluate the effect of plaque composition on stent performance in a carotid artery.CT angiography(CTA)data were used as a reference,and zero-load state of the carotid artery was used to establish a 3D stenotic artery model.Different plaque compositions,calcified and hypo-cellular were defined in Model 1 and Model 2,respectively.Interactions between the stents and arterial tissues within the stent crimping-expansion process were analyzed to explore the effects of plaque composition on the mechanical parameters of carotid stents.Goodman diagram and fatigue safety factor(FSF)were analyzed to explore the effects of plaque composition on fatigue performance of a carotid stent in the stent service process.In the stent crimping-expansion process,the von Mises stress in the stent and the dog-boning ratio in Model 1 were higher than that in Model 2.The calcified plaque prevented the stent from expanding the stenotic vessel to a pre-set diameter.Thus,the risk of rupture in the calcified plaque was higher than that in the hypo-cellular plaque.Plaque also affected the stress/strain in the vessel wall,which was observed to be lower in Model 1 than in Model 2.This indicated that calcified plaque could decrease the stress-induced injury of arterial tissues.Within the stent service process,the stents used in these two models were predicted to not fail under fatigue rupture as calculated by the Goodman diagram.Additionally,the points closer to the fatigue limit were generally observed at the inner bend of the stent crowns.The FSF of the stent in Model 1 was lower than that in Model 2.The stent operating in the presence of calcified plaques suffered high risk of fractures.Reliability and fatigue performance of the stent were found to be associated with plaque composition.Hence,this study may provide stent designers an approach toward enhancing the mechanical reliability of a stent.

Precontoured buttress plate vs reconstruction plate for acetabulum posterior wall fractures: A biomechanical study

BACKGROUND The purpose of open reduction and internal fixation of acetabulum posterior wall fractures is to restore anatomical structure and stability of the hip joint, in order to start weight bearing as soon as possible and prevent hip arthrosis; restoration of the anatomy should preserve function of the joint as well. Although "special shaped precontoured plates" have been developed in recent years for surgical treatment of this region, studies comparing the traditional plates with the newly designed precontoured plates are lacking.AIM To evaluate the biomechanical properties of precontoured anatomic buttress and conventional curved reconstruction plates(CCRPs) for posterior wall acetabulum fracture treatment.METHODS Twelve pelvis models were created for testing plate treatment of fracture in the posterior wall of the acetabulum. These 12 pelvis models were used to create 24 hemipelvis models(experimental) by cutting from the sagittal plane and passing over the center of gravity, after which the posterior wall acetabular fractures(of similar type and size) were created. In these experimental models, the right acetabulum was fixed with a 5-hole CCRP, while the left was fixed with a precontoured anatomic buttress plate(PABP). Samples were placed through thetest device and were subjected to static load testing, with a constant testing velocity of 2 mm/min until the load reached 2.3 kN or the acetabular fixation failed. Dynamic tests were also performed with sinusoidal wave load, with a maximal load of 2.3 kN and a load ratio of 0.1.RESULTS The average stiffness values were 460.83 ± 95.47 N/mm for the PABP and 291.99± 118.58 N/mm for the 5-hole CCRP. The precontoured anatomic acetabulum buttress plates had significantly higher rigidity than the CCRPs(P = 0.022). There was a statistically significant difference between the unloaded and 2.3 kN-loaded values of AL(posterosuperior fracture line vertical to the ground surface) and CL(posteroinferior fracture line vertical to the ground surface) parameters for both the PABPs and the 5-hole CCRPs(P = 0.036 and P = 0.045, respectively).According to the static tests, the amount of total displacement was significantly less in the PABPs than in the CCRPs. Comparative analysis of the displacement in the BL(posterior wall fracture line horizontal to the ground) parameter yielded no statistically significant differences between the PABP and the 5-hole CCRPs(P= 0.261).CONCLUSION PABP provides more stable fixation in acetabulum posterior wall fractures than5-hole CCRP, allowing for proximal or distal fracture line screw application without reshaping.

Corneal biomechanical properties changes after coaxial 2,2-mm microincision and standard 3,0-mm phacoemulsification

AIM： To compare the changes in corneal biomechanics measured by ocular response analyzer （ORA） after 2.2-ram microincision cataract surgery and 3.0-mm standard coaxial phacoemulsification. METHODS： The prospective nonrandomized study comprised eyes with cataract that had 2.2-mm coaxial microincision or 3.0 -mm standard incision phacoemulsification. The corneal hysteresis （CH）, corneal resistance factor （CRF）, corneal-compensated intraocular pressure （IOPcc） and Goldmann-correlated intraocular pressure （IOPg） were measured by ORA preoperatively and at ld, 1-, 2-, 3- and 4-week postoperatively. Results were analyzed and compared between groups. RESULTS： In both groups, CH decreased in the immediate postoperative period （P〈0.05）, returned to the preoperative level at one week （P =0.249） in the 2.2-mm group, and at two weeks in the 3.0-mm group （P --0.264）; there was no significant change in CRF values. In 2.2-mm group, mean IOPcc and IOPg increased at ld postoperatively （both ,P〈0.05）, and returned to preoperative level at one week （,0 =0.491 and P =0.923, respectively）. In 3.0-mm group, mean IOPcc and IOPg increased at ld and lwk postoperatively （P =0.005 and ,P =0.029, respectively）, and returned to preoperative level at 2wk （P =0.347 and P =0.887, respectively）. CONCLUSION： Significant differences between preoperative and postoperative corneal biomechanical values were found for CH, IOPcc and IOPg. But the recovery time courses were different between the two groups. The 2.2-mm coaxial microincision cataract surgery group seemed recovery faster compared to the 3.0-mm standard coaxial phacoemulsification group.

Effects of Blast Wave-induced Biomechanical Changes on Lung Injury in Rats

Objective To observe the dynamic impacts of shock waves on the severity of lung injury in rats with different injury distances.Methods Simulate open-field shock waves;detect the biomechanical effects of explosion sources at distances of 40,44,and 48 cm from rats;and examine the changes in the gross anatomy of the lungs,lung wet/dry weight ratio,hemoglobin concentration,blood gas analysis,and pathology.Results Biomechanical parameters such as the overpressure peak and impulse were gradually attenuated with an increase in the injury distance.The lung tissue hemorrhage,edema,oxygenation index,and pathology changed more significantly for the 40 cm group than for the 44 and 48 cm groups.The overpressure peak and impulse were significantly higher for the 40 cm group than for the 44 and 48 cm groups(P<0.05 or P<0.01).The animal mortality was significantly higher for the 40 cm group than for the other two groups(41.2%vs.17.8%and 10.0%,P<0.05).The healing time of injured lung tissues for the 40 cm group was longer than those for the 44 and 48 cm groups.Conclusions The effects of simulated open-field shock waves on the severity of lung injuries in rats were correlated with the injury distances,the peak overpressure,and the overpressure impulse.

Evaluation of corneal topographic,tomographic and biomechanical indices for detecting clinical and subclinical keratoconus:a comprehensive three-device study

AIM:To evaluate the diagnostic ability of topographic and tomographic indices with Pentacam and Sirius as well as biomechanical parameters with Corvis ST for the detection of clinical and subclinical forms of keratoconus(KCN).METHODS:In this prospective diagnostic test study,70 patients with clinical KCN,79 patients with abnormal findings in topography and tomography maps with no evidence on clinical examination(subclinical KCN),and 68 normal control subjects were enrolled.The accuracy of topographic,tomographic,and biomechanical parameters was evaluated using the area under the receiver operating characteristic curve(AUC)and cross-validation analysis.The Delong method was used for comparing AUCs.RESULTS:In distinguishing KCN from normal,all parameters showed statistically significant differences between the two groups(P<0.001).Indices with the perfect diagnostic ability(AUC≥0.999)were Sirius KCN vertex of back(KVb),Pentacam random forest index(PRFI),Pentacam index of height decentration(IHD),and Corvis integrated tomographic/biomechanical index(TBI).In distinguishing subclinical KCN from normal,Sirius symmetry index of back(SIb;AUC=0.908),Pentacam inferior-superior difference(IS)value(AUC=0.862),PRFI(AUC=0.847),and Corvis TBI(AUC=0.820)performed best.There were no significant differences between the highest AUCs within keratoconic groups(De Long,P>0.05).CONCLUSION:In clinical KCN,all topographic,tomographic,and biomechanical indices have acceptable outcomes in terms of sensitivity and specificity.However,in differentiating subclinical forms of KCN from normal corneas,curvature-based parameters(SIb and IS value)followed by integrated indices(PRFI and TBI)are the most powerful tools for early detection of KCN.

Biomechanical risk factors of non-contact ACL injuries:A stochastic biomechanical modeling study

Significant efforts have been made to identify modifiable risk factors of non-contact anterior cruciate ligament(ACL)injuries in male and female athletes.However,current literature on the risk factors for ACL injury are purely descriptive.An understanding of biomechanical relationship between risk and risk factors of the non-contact ACL injury is necessary to develop effective prevention programs.Purpose:To compare lower extremity kinematics and kinetics between trials with and without non-contact ACL injuries and to determine if any difference exists between male and female trials with non-contact ACL injuries regarding the lower extremity motion patterns.Methods:In this computer simulation study,a stochastic biomechanical model was used to estimate the ACL loading at the time of peak posterior ground reaction force(GRF)during landing of the stop-jump task.Monte Carlo simulations were performed to simulate the ACL injuries with repeated random samples of independent variables.The distributions of independent variables were determined from in vivo laboratory data of 40 male and 40 female recreational athletes.Results:In the simulated injured trials,both male and female athletes had significantly smaller knee flexion angles,greater normalized peak posterior and vertical GRF,greater knee valgus moment,greater patella tendon force,greater quadriceps force,greater knee extension moment,and greater proximal tibia anterior shear force in comparison to the simulated uninjured trials.No significant difference was found between genders in any of the selected biomechanical variables in the trials with simulated non-contact ACL injuries.Conclusion:Small knee flexion angle,large posterior GRF,and large knee valgus moment are risk factors of non-contact ACL injury determined by a stochastic biomechanical model with a cause-and-effect relationship.Copyright(c)2012,Shanghai University of Sport.Production and hosting by Elsevier B.V.All rights reserved.

Biomechanical behavior study of dog‘s small intestines

The biomechanical behavior of dog's duodenum and jejunum were studied and a formulation of the stress strain relation is presented in this paper. The results obtained indicated that the exponential coefficient α and the incremental duodenum of the elastic modulus are both larger than those of the jejunum. It means that the duodenum is more deformable than the jejunum. The experimental results of this work provide basal data for kinematics study of a robotic endoscope.

Biomechanical Mapping of the Female Pelvic Floor: Prolapse versus Normal Conditions

Background: Quantitative biomechanical characterization of pelvic supportive structures and functions in vivo is thought to provide insight into pathophysiology of pelvic organ prolapse (POP). An innovative approach—vaginal tactile imaging—allows biomechanical mapping of the female pelvic floor to quantify tissue elasticity, pelvic support, and pelvic muscle functions. The Vaginal Tactile Imager (VTI) records high definition pressure patterns from vaginal walls under an applied tissue deformation and during pelvic floor muscle contractions. Objective: To explore an extended set of 52 biomechanical parameters for differentiation and characterization of POP relative to normal pelvic floor conditions. Methods: 96 subjects with normal and POP conditions were included in the data analysis from multi-site observational, case-controlled studies;42 subjects had normal pelvic floor conditions and 54 subjects had POP. The VTI, model 2S, was used with an analytical software package to calculate automatically 52 biomechanical parameters for 8 VTI test procedures (probe insertion, elevation, rotation, Valsalva maneuver, voluntary muscle contractions in 2 planes, relaxation, and reflex contraction). The groups were equalized for subject age and parity. Results: The ranges, mean values, and standard deviations for all 52 VTI parameters were established. 33 of 52 parameters were identified as statistically sensitive (p 0.05;t-test) to the POP development. Among these 33 parameters, 11 parameters show changes (decrease) in tissue elasticity, 8 parameters show deteriorations in pelvic support and 14 parameters show weakness in muscle functions for POP versus normal conditions. Conclusions: The biomechanical mapping of the female pelvic floor with the VTI provides a unique set of parameters characterizing POP versus normal conditions. These objectively measurable biomechanical transformations of pelvic tissues, support structures, and functions under POP may be used in future research and practical applications.

Human umbilical cord blood stem cells and brainderived neurotrophic factor for optic nerve injury: a biomechanical evaluation

Treatment for optic nerve injury by brain-derived neurotrophic factor or the transplantation of human umbilical cord blood stem cells has gained progress, but analysis by biomechanical indicators is rare. Rabbit models of optic nerve injury were established by a clamp. At 7 days after injury, the vitreous body received a one-time injection of 50 μg brain-derived neurotrophic factor or 1 × 10^6 human umbilical cord blood stem cells. After 30 days, the maximum load, maximum stress, maximum strain, elastic limit load, elastic limit stress, and elastic limit strain had clearly improved in rabbit models of optical nerve injury after treatment with brain-derived neurotrophic factor or human umbilical cord blood stem cells. The damage to the ultrastructure of the optic nerve had also been reduced. These findings suggest that human umbilical cord blood stem cells and brain-derived neurotrophic factor effectively repair the injured optical nerve, improve biomechanical properties, and contribute to the recovery after injury.

Study of corneal biomechanical properties in patients with childhood glaucoma

AIM:To study of corneal biomechanical properties and intraocular pressure(IOP)measured with Corvis Scheimpflug Technology(ST)in patients with childhood glaucoma(CG).METHODS:Cross-sectional study in which 89 eyes were included 56 of them with CG.Only one eye per patient was included.The following variables were obtained from the clinical history and the ophthalmological examination:age,sex,IOP,number of surgeries,and the cup/disc ratio(CDR).The following parameters were recorded using Corvis ST:corrected by biomechanics IOP(b IOP),not corrected IOP(nct IOP),central corneal thickness(CCT),maximum concavity[radius,peak distance(PD)and deformation amplitude],applanation 1 and 2(length and velocity).The mean age was 23±14.55 and 33±19.5 years old for the control group and CG group,respectively.Totally 36 were males and 53 were females.In the CG group,7 patients were controlled only with medical treatment.Sixteen had at least one previous goniotomy,19 had at least one trabeculectomy,and 11 had an Ahmed implant.RESULTS:A significant and positive intraclass correlation coefficient was found between Goldman IOP and the IOP measured by Corvis in both groups.No differences were found between the IOP measured with Corvis and Goldman using a student t-test.Regarding biomechanical parameters,there were differences in the applanation length 2(A-L2),in the applanation velocity 2(A-V2)and in the PD.By sex,only the applanation length 1(A-L1)was found to be different in control group.A positive and significant Pearson correlation was found between CDR and the A-L1.CONCLUSION:Corneal biomechanical properties have shown differences between CG and healthy subjects and also between men and women.

Biomechanical Manifestations of Diastolic and Systolic Function in Rats with Heart Failure with Preserved Ejection Fraction

Objective Heart failure(HF)is divided into two types:Heart failure with reduced ejection fraction(HFrEF)and heart failure with preserved ejection fraction(HFpEF).The latter always results in diastolic dysfunction,characterized by changes in mechanical properties.The objective of this study is to build a finite element(FE)model of HFpEF and analyze diastolic and systolic function in rats.Methods Ten Dahl salt-sensitive rats were fed either a low-salt(LS)(n=5)or highsalt(HS)(n=5)diet beginning at 7 weeks of age and scanned by ultrasonic machine at 14 weeks of age.A non-linear FE model of the left ventricle(LV)was built from cardiac echo images at end-diastole and passive material properties of the LV were prescribed using Fung’s transversely isotropic constitutive law.Fiber angles of the endocardium and epicardium were prescribed as 53°°and-52°,respectively,with respect to the circumferential direction and varied linearly through the LV wall.The method developed by Krishnamurthywas used to determine the unloaded geometry to estimate the Fung passive material parameters.LV end-diastolic pressure(EDP)was determined from the measured pressure waves and applied to the endocardium at the unloaded geometry to simulate passive filling.Active material properties of the LV were prescribed using Guccione’s time-varying elastance model and maximum isometric tension was scaled to match the measured peak systolic pressure.The finite element model was then coupled to the Windkessel model,whose parameters were adjusted to the measured hemodynamics.Results Measured LVEDPs of LS and HS rats were 4.9±3.4 mmHg and 13.2±5.4 mmHg(P-0.030 8),respectively.End-diastolic Cauchy stress along the fiber direction for LS rats was significantly lower than for HS rats(0.91±0.60 kPa vs 3.00±0.63 kPa,P=0.001 4)and there was a similar trend in end-diastolic Green Strain along the fiber direction(0.058±0.003 vs 0.072±0.010,P=0.012 8,Figure 1b),as well.There was no distinctive difference between end-systolic Cauchy stress along the fiber direction for LS rats and HS rats(17.2±4.3 kPa vs 17.2±5.5 kPa,P=0.991 9)but end-systolic Green Strain along the fiber direction for LS rats was significantly higher than for HS rats(-0. 108±0.017 vs-0.065±0.024,negative sign represents direction).Conclusions For rats with HFpEF,it is the elevated LVEDP that induces the increase in end-diastolic stress and strain,thereby leading to diastolic dysfunction.Because of the preserved ejection fraction,HFpEF has less effect on systolic function.

Biomechanical Design in Osteogenic Engineering

The bone is a naturally occurring composite system comprising collagen matrix and hydroxyapatites capable of generating sufficient strength and toughness to support mechanical loads and resist fracture,respectively.The material strength depends largely on the elastic properties,whereas the toughness depends on not only the elastic,but also the plastic properties.Thus,both elastic and plastic properties must be considered in the analysis of bone biomechanics and the design of osteogenic materials.The bone is capable of optimizing its elastic and plastic properties by integrating stiff hydroxyapatites and ductile collagen fibrils into a hierarchically ordered architecture,an effective mechanism to support the bone strength and toughness.Such a mechanism can be used as a model for designing osteogenic materials.

Biomechanical modeling for the response of human thorax to blast waves

A simplified finite element model of a human thorax had been developed for probing into the mechani- cal response in simple and complex blast environments. The human thorax model was first created by CT images with blast loading applied via a coupled arbitrary Lagrangian- Eulerian method, allowing for a variety of loads to be considered. The goal is to analyze the maximum stress distri- butions of lung tissue and peak inward thorax wall velocity and to know the possible regions and levels of lung injury. In parallel, a mathematical model has been modified from the Lobdell model to investigate the detailed percentage of lung injury at each level. The blast loadings around the human tho- rax were obtained from the finite element model, and were then applied in the mathematical model as the boundary con- ditions to predict the normalized work of the human thorax lung. The present results are found in agreement with the modified Bowen curves and the results predicted by Axels- son＇s model.

Intraprosthetic fixation techniques in the treatment of periprosthetic fractures: A biomechanical study

AIM: To develop new fixation techniques for the treatment of periprosthetic fractures using intraprosthetic screw fixation with inserted threaded liners. METHODS: A Vancouver B1 periprosthetic fracture was simulated in femur prosthesis constructs using sawbones and cemented regular straight hip stems. Fixation was then performed with either unicortical locked-screw plating using the less invasive stabilization system-plate or with intraprosthetic screw fixation using inserted liners. Two experimental groups were formed using either prostheses made of titanium alloy or prostheses made of cobalt chrome alloy. Fixation stability was compared in an axial load-to-failure model. Drilling was performed using a specially invented prosthesis drill with constantly applied internal cooling.RESULTS: The intraprosthetic fixation model with titanium prostheses was superior to the unicortical lockedscrew fixation in all tested devices. The intraprosthetic fixation model required 10 456 N ± 1892 N for failure and the unicortical locked-screw plating required 7649 N ± 653 N(P < 0.05). There was no significant difference between the second experimental group and the control group.CONCLUSION: Intraprosthetic screw anchorage with special threaded liners enhances the primary stability in treating periprosthetic fractures by internal fixation.

Biomechanical study of modular hemipelvic endoprosthesis for Type I-IV defect of pelvic tumor

Background： The modular hemipelvic prosthesis has been used in patient of Type I-IV pelvic tumor with good outcomes, but how to keep the stability between the prosthesis and the residual sacrum is a problem. An additional screw-rod system seems to solve it, but its biomechanical characters are still not well understood, which need experimental evaluation. Methods： Six pelvic specimens were prepared in three conditions （normal intact pelvis, ＂normal＂; the pelvis of left Type I-IV defect and implanted with prosthesis without/with additional screw-rod system, ＂rod-＂ and ＂rod＋＂）. Compressing biomechanical experiments （50-500N） were performed in these three conditions, respectively. Results： The loadings during the experiments are in accordance with the linear elastic control mode. Under the increasing loading, the implanted pelvises displaced asymmetrically, unlike normal intact pelvis. The vertical displacement of ＂rod＋＂ changed significantly, whereas ＂rod-＂ did not. For both implanted pelvis, right side displaced less than left side （P values 〈0.05）. Conclusions： The implanted pelvis showed asymmetric displacement under loading, where healthy side displaced more. The implanted pelvis plus screw-rod system showed less displacement at implanted side but more at contralateral side in comparison with those without screw-rod system.

Biomechanical features of Poly-D,L-lactic acid (PDLLA) rods through the degradation in vitro and in vivo

Objective：To observe the changing of biomechanical features during the degradation course of poly-D,L-lactic acid （PDLLA） rods in vivo and in vitro and to evaluate its value as an internal fixation material. Methods ：PDLLA rods were emerged into PBS simultaneous body fluid with constant temperature of 37℃ and the rods were embedded into muscle tissue of 20 rabbits for degradation in vitro and in vivo . The rods were taken out in 2, 4, 6, 8 and 12 weeks. Biomechanical features of bending, shearing and axial compression strength, rigidity and elastic modulus were observed during the degradation course. Statistical method was used to test the changes of biomechanical parameters. Results： （1）There was similar changes of bending, compressive, shearing strength and bending, compressive and shearing rigidity of the PDLLA rods between in vivo and in vitro. （2）Bending, compressive, shearing strength decreased 33%, 18 % and 43 % respectively within the first stage of the degradation, and after 6 weeks of degradation, they decreased slowly. （3）Elastic modulus, bending, compressive and shearing rigidity.decreased sharply during the 6 weeks of degradation, with a drop of 22%, 39% and 30% respectively, and after 8 weeks, they decreased slowly. Even after 12 weeks of degradation, the strength of the rods was still higher than that of sponge bone. Conclusion： During the degradation of the material, the strength and rigidity of PDLLA rods can meet the need of fracture fixation of cancellous bones.